1. Field of the Invention
The present invention is directed to a multi-electrode negative ion generator which in addition to the ion emitting electrode may include one or two additional electrodes with voltages being supplied by the generator to control the negative ion emission.
2. Description of Background Art
With regard to the use of a negative ion generator (NIG) if the cabinet for housing the NIG is a grounded metal cabinet, then all the ion current from the emitter is collected on the metal cabinet and little, if any passes through the openings of the screen.
As a result most ion generators developed for domestic use, which are generally in insulating cabinets, produce a very low output of negative ions. To produce any significant ion current output, the pointed high voltage electrode is placed very close to the aperture of an insulating screen. In some instances, this high voltage tip can be contacted easily with fingers through the screen.
If a NIG is housed in a plastic cabinet and the ion source is placed at a short distance behind the plastic screen, then negative charge accumulating on the screen will ultimately develop a potential equal to that on the discharge source. When this occurs, the ion emission from the unit drops to negligible value. For example, when a free standing point emitting about 1000 nanoamps (1 microamp or 1 millionth of an ampere) of ion current is placed within a plastic cabinet, the ion emission detected outside the cabinet quickly drops by a factor of 1000 to less that 1 nA. This is particularly so when the location of the ion emitter is sufficiently remote from the cabinet screen (about 10 mm) to satisfy UL requirements.